trace deprecation option in node

I recently spent a bit of time trying to upgrade our internal toolkit at rexlabs to the latest versions of webpack, babel, jest and storybook. Naturally, e.g. upgrading webpack from v 2.x to 4.x, a lot of the API changed and a lot of plugins needed (or still need) to change.

As a result of that, I found myself going through heaps of deprecation warnings in the process. Manually disabling and enabling plugins in order to find out which ones were causing the issues, until I stumbled accross a comment on one of the github issues: https://github.com/webpack/loader-utils/issues/75#issuecomment-285637755

-​-trace-deprecation

Well, turns out there is a node option to easily show where the deprecation warning is coming from. Wish I'd known that 4 hours earlier 😅

In any way, by simply adding it to the command you get super helpful stack traces with your warnings:

# e.g. before
myscript build
# ^ throws a bunch of deprecation warnings

node --trace-deprecation myscript build
# ^ still throws the warnings, but now includes stack traces for them

You can even activate it within your node script, by setting the following process variable, simply utilising nodes internal deprecation mechanisms:

// in your node script before running whatever is causing the warnings
process.traceDeprecation = true;

🤯